This application claims the priority of German Patent Document 199 41 133.6, filed Aug. 30, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention concerns a constructed nozzle ring for a gas turbine, more particularly for an aircraft engine, comprising a shroud with a circumferential surface and at least one blade with a surface, with the shroud having at least one opening for fastening the blade, the circumferential surface of the shroud facing the blade, and the blade having on at least one end section a platform which has at least in part a transition curve which projects above its surface and which is inserted in the opening.
Constructed nozzle rings are integral components which generally comprise a ring-shaped outer shroud, several blades, and in some cases a ring-shaped inner shroud. Nozzle rings of this kind can also be constructed in segments and are used by way of example in condensers of aircraft engines. The shroud generally extends around the longitudinal axis of the gas turbine. The blades are essentially arranged in radial direction.
In a known constructed nozzle ring, the blade has at least one end section with a constant profile or a constant cross-sectional area which is inserted in an opening formed in the shroud during assembly and is fastened through soldering or welding for example. The blade can also have a constant profile or a constant cross section at an opposite, second end section and be inserted in a second shroud, i.e., an exterior and interior shroud. A drawback to this is that while the profile of the blade does not have to be constant over the entire channel height, it is nevertheless restricted with respect to its profile geometry for assembly reasons. The blade for example cannot have a sharp bend or pronounced increase in thickness in the area situated between the end sections. In addition, the openings in the area of the inlet and outlet edges may be very slim in the case of narrow shovel geometry, which creates problems in manufacture.
Known from German Patent Document DE-AS 12 00 070 is a manufacturing method for a vane ring in which the footings of the blades are inserted in grooves formed in a ring body, whereby the blade transitions with a curve into the blade footing and the ring body is separated at the end into several segments.
European Patent Document EP 0 704 602 A2 discloses turbine blades arranged on a carrier in which the surface of the blade transitions radially into the circumferential surface of the carrier.
Furthermore a manufacturing method for a vane is known from European Patent Document EP 0 199 073 A1 which is fastened to a stator through soldering, whereby the vane is manufactured from an oversized profile bar and whereby a foot-like thickening is upset into the profile bar at at least one end in order to increase the soldering surface and in this area a soldering surface is formed. For the incidence of the vanes, the profile bar can be upset diagonally on one side.
An object of the present invention is to create a constructed nozzle ring of the type described above which provides savings in the overall axial length, can be manufactured as simply as possible, and is subjected to no or only slight restrictions with respect to profile geometry of the blade, for example for installation reasons.
The solution of the object according to the invention is characterized in that the platform in the area of an inlet and/or outlet edge of the blade projects over the surface of the blade less than in the middle area of the blade and thus overall axial size is reduced.
The circumference of the platform can be adapted to a circumference of the blade which is situated radially in an area opposite the tip of the blade so that the distance between said two circumferences is essentially constant except in the area of the inlet and/or outlet edge.
The transition curve can be configured increasingly narrower from a middle area of the blade in the direction of the inlet and/or outlet edge. Alternatively, the blade in the area of the inlet and/or outlet edge can have no platform projecting above its surface.
The advantage of such a constructed nozzle ring is that as a result of the additionally provided platform, the coupling of blade and shroud is possible without restriction with respect to the profile geometry of the blade. In addition, the platform, which is provided with a transition curve, provides advantages with respect to aerodynamics and strength. The openings in the shroud have larger radii in the area of the inlet and outlet edge and are easier to fabricate.
In one configuration, the transition curve conforms to the surface of the blade and to the circumferential surface of the shroud which borders the platform in assembled condition for optimal shape with respect to aerodynamics and strength.
In addition, the blade in the area of the inlet and/or outlet edge can have no platform over the circumference of such edge as a result of which the overall axial length of the nozzle ring is further reduced. Since the platform in addition with its circumference runs out in the inlet and/or outlet edge on both sides, the problem of the too narrower or difficult to manufacture edges in the openings of the shroud does not occur.
In the case of no platform, the surface of the blade in the area of the inlet and/or outlet edge in assembled condition can border the circumferential surface of the shroud, whereby in the remaining area along the circumference of the blade, for example in the middle area on the suction and pressure sides, there is a platform with a transition curve projecting above the circumference of the blade.
The transition curve can alternatively be configured increasingly narrow from a middle area of the blade, for example on the suction and pressure side, in the direction toward the inlet and/or outlet edge so that as a result of the narrower curve in the area of the inlet and/or outlet edge overall axial length is reduced.
The transition curve can be configured in a circular shape at least in part and have a radius whereby in the middle area of the blade it is larger than in the other areas along the circumference of the blade. If the blade has a platform along the entire circumference which projects above its circumference, the radius is thus smallest in the area of the inlet and/or outlet edge in order to reduce the overall axial length.
In a constructed nozzle ring, the radius along the circumference of the blade can be constant and its middle point can be modified such that the transition curve conforms along the entire circumference to the surface of the blade and there is a tangential jump to the circumferential surface of the shroud at the inlet and/or outlet edge. Manufacture with constant radius is favorable. In addition, as a result of the tangential jump at the inlet and/or outlet edge, which to that point can increase successively, the overall axial length of the nozzle ring is reduced.
Additional preferred exemplary embodiments of the invention are described in the subclaims.